There have been proposals in the prior art for the destruction of vegetation around and between railroad tracks by the application of electricity to the vegetation, such as shown in U.S. Pat No. 546,682, however, such prior proposals have been impractical and are not in use commercially. Commercially, plants growing around and between railroad tracks are destroyed by spraying chemicals on the plants, and while this method is effective it is relatively expensive and there can be adverse environmental effects on the surrounding land, especially where the tracks pass through cropland. According to the present invention, a specific structure is provided that is eminently suitable for killing plants around and between railroad tracks, and which is commercially feasible. Also, according to the present invention a more general method and apparatus are described for preventing damage to the high voltage source despite the fact that the actual plant contacting means associated with the plant destruction device pass through areas of greatly differing plant density, by limiting the current output of the high voltage electricity source for plant destruction; and the number of fires in dry material associated with plants being contacted are minimized by reducing the no-load voltage of the high voltage source to generally the same level as the full-load current limited voltage thereof. While the current-limiting and no-load voltage controlling aspects of the present invention are particularly useful for destruction of plants in and around railroad tracks, they also have general applicability to plant destruction in general, such as is provided by U.S. Pat. No. 3,919,806, and copending application Ser. No. 795,087, filed May 9, 1977.
According to one aspect of the present invention, a machine for destroying plant growth around and between a pair of railroad tracks is provided. The machine comprises a vehicle having at least two sets of wheels adapted to ride on the tracks, the wheels of each set being electrically isolated from each other, and a source of high voltage electricity mounted on and movable with the vehicle. Means are provided for connecting the high voltage source of electricity to ground, including through one wheel of at least one of the wheel sets. Means are provided for destroying plants around and between the railroad tracks, such means including a generally horizontally disposed rod mounted on the vehicle, plant contacting means operatively connected to the rod, and means for operatively electrically connecting the plant contacting means to the high voltage source, the plant contacting means transferring electricity from the high voltage source to ground through the plants contacted thereby. The plant contacting means may comprise a plurality of vertically disposed chains connected to the rod outside the tracks, and a plurality of downwardly extending support rods connected to the horizontal rod and having leaf spring plant contactor members connected thereto. Alternatively, in order to reduce arcing by minimization of the voltage gradient in close proximity to the plant contacting surface, the plant contacting means may comprise a plurality of rounded-end generally cylindrical contacting members having the longitudinal axes thereof disposed generally perpendicular to the direction of movement of the vehicle. Such cylindrical members are operatively connected to the horizontally disposed rod by spring members, and a generally triangular plate mounted between each spring member and the corresponding cylindrical member, and bolts or the like for mounting the spring member to the generally horizontal rod. The end portions of the horizontal rod extending past the railroad tracks may be pivotally mounted to the middle portion of the rod so that the end portions may pivot out of the way of unyielding obstructions which might be engaged thereby, but will return to their original position after the obstruction in past. Their original position may be at an angle .alpha. of about 15.degree. in back of the middle portion. Additionally, the cylindrical members may be staggered in the dimension of movement of the vehicle so that loose material in the path thereof can pass between adjacent cylindrical members, and the end portions of the generally horizontally extending rod can be mounted for pivotal movement about a generally horizontal axis from a position about 90.degree. above the middle portion, to a position about 45.degree. below the middle portion of the generally horizontally extending rod.
According to another aspect of the present invention, a machine for destroying plants with electricity is provided comprising a high voltage source of electricity, electrically conductive means adapted to be operatively mounted to a vehicle for movement with the vehicle, and for transferring electricity from the high voltage source to ground through plants to be destroyed thereby, and means for limiting the current output of the high voltage source so that damage to the high voltage source is prevented even during extended operation of the machine. The high voltage source may comprise a fossil-fuel powered electric generator, a generally stable voltage electric power source, a voltage regulator operatively connected to the generally stable voltage electric power source and to an excitor field for the fossil-fuel power generator, and a step-up transformer operatively connected to the high voltage generator. The current limiting means then comprises a variable resistor operatively connected between the voltage regulator and the excitor field. Additionally, the machine may further comprise means for controlling the no-load voltage of the high voltage source to a maximum level so that the number of fires started during the no-load situation in material around the plants being treated are minimized. Such controlling means may comprise a variable transformer disposed in a sensing circuit for the voltage regulator, the transformer capable of reducing the no-load voltage to generally the same level as the full-load current limited voltage.
According to yet a further aspect of the present invention, a method of destroying plants is provided comprising providing a high voltage source of electricity, operatively connecting the source to plant contacting means, contacting the plants to be destroyed with the plant contacting means, regulating the voltage of the high voltage source, and controlling the no-load voltage of the source so that it is substantially the same as the full-load voltage of the source. A method of destroying plants is also provided comprising the steps of providing a high voltage source of electricity, operatively connecting the source to plant contacting means, contacting plants to be destroyed with the plant contacting means, and regulating the voltage of and limiting the current output of the high voltage source so that damage to the high voltage source is prevented even during extended operation.
It is the primary object of the present invention to provide improved methods and apparatus for destroying plant growth with electricity. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.